revert: "refactor!: drop e-invoicing integration from erpnext (#26940)"

This reverts commit c335962827.

erpnext/controllers/accounts_controller.py

@@ -167,9 +167,14 @@ class AccountsController(TransactionBase):
 
 		validate_regional(self)
 
+		validate_einvoice_fields(self)
+
 		if self.doctype != 'Material Request':
 			apply_pricing_rule_on_transaction(self)
 
+	def before_cancel(self):
+		validate_einvoice_fields(self)
+
 	def on_trash(self):
 		# delete sl and gl entries on deletion of transaction
 		if frappe.db.get_single_value('Accounts Settings', 'delete_linked_ledger_entries'):
@@ -2151,3 +2156,7 @@ def update_child_qty_rate(parent_doctype, trans_items, parent_doctype_name, chil
 @erpnext.allow_regional
 def validate_regional(doc):
 	pass
+
+@erpnext.allow_regional
+def validate_einvoice_fields(doc):
+	pass